The present invention relates to a vessel for DC arc furnaces with consumable elements serving as bottom electrodes which are fastened to the jacket or jacket portion that defines the vessel bottom; the electrodes project into the interior of the furnace which is otherwise lined with a refractory material, and directly engage the molten metal in the hearth portion of the furnace, whereby the consumable elements are connected with cooling sleeves provided with an interior space for being flown through by a cooling medium, and being further provided with connections for the feeding of electrical current.
European printed patent application No. 58 817 discloses a furnace generally of the type to which the invention pertains, and wherein particularly contact devices are provided for the anode in the central portion of the vessel bottom. These contact devices are comprised of a plurality of metal pins being held in the refractory and fireproof lining, and running in parallel to the axis of the vessel. The fireproof lining of the vessel and the metal pins will become extremely hot during operation and, therefore, wear very quickly and severely. The wear is, of course, locally limited as far as the individual electrodes are concerned, which means that as far as the overall electrode structure is concerned in each instance, there is a very unequal thermal load, and that poses the danger of penetration. Generally speaking the problem of excessive heating of these parts has been counteracted by intensive cooling, but it is not believed that this is sufficient.
The aforementioned patent application No. 58 817, moreover, discloses contact electrodes, wherein the necks of the electrodes are cooled by a fluid. There is, of course, the danger of instant evaporation on contact with the molten material, if the cooling medium is water. Therefore, one uses occasionally or even frequently, air for cooling purposes, but air is, in fact, a very poor coolant considering the severe thermal conditions under which these electrodes must operate.
Alternatively, the German printed patent application No. 26 37 632 describes a very elaborate system for discovering local points of melting at the head of the bottom electrodes. These particular bottom electrodes, however, are disadvantaged by the fact that a corrective measure can be undertaken only after, in fact, some local defect has occurred, and only then can further destruction of the electrode be avoided. But the onset of this local defect is not discoverable directly.
European patent application No. 12 050 describes arc furnaces, wherein instead of water or air as a coolant, one uses mercury, potassium, or sodium. These fluids, however, have the disadvantage that they do, in fact, solidify well above room temperature, and if that occurs, they will, of course, impede the coolant flow.